Do you experience problems during downloading?
Check your connection in Status and Interface settings window.
Use Test Server in Config > Servers.
We will probably ask you to do a test using only basic settings.

Do you experience problems during repair or unpacking?
Enable +Debug logging in the Status and Interface settings window and share the relevant parts of the log here using [ code ] sections.

Recently I learned about "screen". I find it handy in combination with SABnzbd, so here's a FYI:

If you want to keep SABnzbd running in a terminal, but not as a service/daemon, you can do that with "screen":

With SSH / putty, connect to your Linux machine. Type "screen", and you get a new terminal. There type "sabnzbdplus", and see SAB starting and running. Good.
Now the magic: type "CTRL A D" (detach?), and you're back in the first terminal. You can disconnect. SABnzbd is still running.

Then, later on, with SSH/putty reconnect to your Linux machine. Type "screen -ls" to see the running screen processes. If there is only one, you can type "screen -ar" (reconnect?) to reconnect. You get the SABnzbd process again.
Type "CTRL A D" to detach again.